Humans generally find it useful or entertaining to view images or projections of visual representations of real or imaginary things. Therefore, technologies have been developed to enable us to place visual representations, such as still images and moving images, onto surfaces or screens so that we can enjoy or benefit from such visual displays.
One common depiction used for educational and recreational purposes is to depict the surface of planet Earth so that people can observe the various bodies of land and water thereon. Earth depictions can be in the form of photographs, illustrations, or other visual means. More realistic representations of Earth, the Moon, planets, anatomical structures, or other three-dimensional objects have been created by painting the image of the same onto a spherical or other three-dimensional shell or globe. The classic spinning globe atlas of Earth that can spin along a North-South axis is a standard feature in libraries, offices and homes. Medical institutions and instructional classrooms have benefited from drawn representations of anatomical features or organs (e.g., the brain) so that practitioners and students can get a clearer understanding of the structure of the organs. However, such representations usually are artists' drawn renditions, and may not have the desired or required level of detail. Also, such three-dimensional solid models lack a dynamic character that would allow the depiction of an image of an object in real time. In addition, it is difficult or impossible to selectively add or delete desired features or layers to such representations at will.
More realistic or dynamic representations of the surface of Earth have been used in products such as Google Earth from Google, Inc. of Mountain View, Calif. This product and others portray photographic images of the Earth onto computer monitor screens, giving the user the feeling of seeing the Earth from some height, either perpendicular to the terrain or at some angle thereto. However, the image is displayed on whatever display surface the user's computer monitor is using, which is generally flat or substantially two-dimensional. This is a general weakness in depicting naturally three-dimensional (e.g., spherical) objects onto flat, two-dimensional, projection surfaces.
Examples of visual projection display technologies include flat sheets of white or reflective material onto which an appropriate image is projected. These are commonly called “projection screens.” This technique for illuminating a screen can be carried out on a suitable blank wall as well, and is the basis for common cinema projection displays, home slide show displays, outdoor wall displays, etc. The principle of operation of such displays is directing a focused image (still or moving) onto the projection screen or surface. The image is then reflected off the screen or surface so that it can be seen by observers on the same side of the projection screen plan as the device projecting the image onto the screen. Some drawbacks to this technology include that the projector device (e.g. movie or slide projector) and the screen are two distinct (usually large) pieces of equipment that require focusing and aiming of the projector onto the surface of the screen. Also, in such systems, as the projector and the viewing audience are on the same (illuminated) side of the projection screen the audience may be disposed between the projector and the projection screen. This requires special care so that the projector is not illuminating its audience from behind, and casting a shadow onto the projection screen, resulting in the well-known “down, in front!” complaint from the rest of the audience trying to enjoy the image. In these systems, the image can be said to be frontally projected onto the screen because the incident light from the projector device is reflected off of the frontal face of the projection screen, and both the projector (light source) and the viewer are on the same (frontal) side of the projection screen.
Another example of visual projection display technologies includes television sets and computer monitors and similar devices. Here, an image is projected from the “back” face of the screen and instead of being reflected off the screen, is scattered by the screen material and travels through the screen to the eye of the beholder. Such screens are illuminated through “back projection” by a projector or source of light that is on the opposite side or face of the screen than the viewers looking at the image on the screen. Therefore, these systems do not suffer from the viewer him or herself interfering with the path of light projected from the projector onto the screen.
Present back-projection systems typically project computer-controlled colored light onto a screen capable of scattering the projected light to form the image on the screen. Present systems require focusing and are generally projected onto flat surfaces or nearly flat surfaces, such as computer monitors or television screens. Some prior art includes back projection onto a non-flat screen, however, these prior systems suffered from limited clarity and focusing problems because the light used by their projectors was not coherent. Also, these prior systems lacked a true range to cover a substantial three-dimensional projection screen because of the cumbersome mechanisms that had to be installed on the side of the screen facing the projector, thereby limiting the solid angle that could be displayed on the projection screens of traditional back projection systems. Also, prior systems were generally incapable of producing dynamic images and more complex and interesting or useful images, and in many case were only capable of providing static or quasi-static images on the screens. In addition: presently available coherent light projection systems generally only scan a coherent light source over the projection surface, and don't include appropriate modulation components for the applications discussed below. In addition, present systems can require excessive power and cooling mechanisms that are not practical desirable, or possible in the applications as discussed below.
Some present systems purport to project images onto a convex mirror that is mounted inside of a projection screen, the mirror being in a predetermined position facing the projector. This approach fails to achieve a proper focus over the extended projection screen due to the varying image distance in relation to the screen and the convex mirror geometry. Also, in existing systems of this type, the size of the screen cannot be changed without adjusting the mirror and the optics, which is not possible and/or not practical or cost effective. Also, the solid angle that could be displayed on the projection screen is limited by the mirror, which casts a distracting shadow that detracts from the projected image.
Other present systems require the use of custom optics to achieve a variable focal distance to attempt to match the corresponding distance from the image projector to the three-dimensional screen. This method displays images in fair focus at closer range, eliminating the shadow. However, numerous limitations of this type of projection system have not been overcome. For example, it is not possible to substantially cover a spherical or other substantially enclosed three-dimensional screen with a clear true focused image using this system. Furthermore, when alterations are made to the screen size, distance, or shape, corresponding custom alterations would also be required to be made to the lens in order to function properly. Such custom lens design is not available and/or not practical or cost effective, therefore, these systems cannot satisfy a need for a variable-focal length projection coverage of a three-dimensional screen.
The systems described above typically employ a conventional non-coherent light source such as a UHP lamp. Conventional non-coherent projector systems require collocation of their incident light beams to form a clear, sharp, focused image onto the projection surface, and a focused image is generally formed in one plane at a given distance from the projector.
Other existing systems project light into an expensive and cumbersome inflatable balloon by means of a fiber optic tether, which carries light and power to a scanning deflector module and projection head. Limitations of this system include its undesirable size, cost, safety concerns, reliability, and efficiency. These systems use mixed gas lasers which deliver very high amounts of laser energy in the visible spectrum. As a result they require a very high electrical power input and a commensurate cooling capability to prevent overheating. These systems also require a three-phase power supply, 220 volt circuit running on a 45 A breaker per phase. This system also has a very high discharge current and is extremely costly to own and maintain.
The cost to own a ion laser is tens of thousands of dollars annually. Mixed gas lasers also emit a very large amount of heat requiring a continuous water supply for cooling. By combining water and high voltage together in the same unit, a mixed gas ion laser puts the user at great risk of electrical shock.
This system is also very bulky, needing roughly 9.5 cubic feet of space and weighing over 200 lbs. Ion Laser tubes contain Beryllium Oxide, which is carcinogenic if ingested or inhaled, so extreme care must be taken when handling this type of device.
These types of lasers are currently used in commercial laser light shows, and are the preferred laser types for such displays due to the high output. In a large scale multimedia display such as a stadium, great care must be taken to ensure the safety of the observers. The inner workings of the system must be off limits to people unless properly trained to handle such equipment.
There is a need for a three-dimensional back-projection display system that can overcome inter alia, the limitations of the prior art by eliminating focal difficulties, cumbersome mirror assemblies, custom optics requirements, costly and impractical light source cooling, and distracting shadows cast onto the display surface.